# Rigour, Proof and Soundness

• Oliver M W Tatton-Brown

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

### Abstract

The initial motivating question for this thesis is what the standard of rigour in modern mathematics amounts to: what makes a proof rigorous, or fail to be rigorous? How is this judged? A new account of rigour is put forward, aiming to go some way to answering these questions. Some benefits of the norm of rigour on this account are discussed. The account is contrasted with other remarks that have been made about mathematical proof and its workings, and is tested and illustrated by considering a case study discussed in the literature.

On the view put forward here one can obtain a manner of informal, rigorous mathematics founded on any of a variety of proof systems. The latter part of the thesis is concerned with the question of how we should decide which of these competing proof systems we should base our mathematics on: i.e., the question of which proof system we should take as a foundation for our mathematics. A novel answer to this question is proposed, in which the key property we should require of a proof system is that for as many different kinds of structures as possible, when the proof system allows a generalization about that kind of structure to be proved, the generalization actually holds of all real examples of that kind of structure which exist. This is the requirement of soundness of the proof system (for each kind of structure). It is argued that the best way to establish the soundness of a proof system may be by giving an interpretation of its axioms on which they are established as true. As preparation for this discussion, the thesis first investigates the logical and conceptual basis of various arithmetic concepts, with the results obtained used in the final discussion of soundness.
Date of Award 12 May 2020 English University of Bristol Arts and Humanities Research Council Catrin Campbell-Moore (Supervisor) & Philip D Welch (Supervisor)

• Philosophy
• Mathematics
• Rigour
• Proof
• Soundness
• Arithmetic
• Logic
• Knot Theory

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